1. Field of the Invention
This invention relates to the field of lighting controls and more particularly to two terminal, direct current incandescent lamp dimmers used for illumination level and electrical current level control.
2. Description of Prior Art
A number of methods for dimming incandescent lamps have been disclosed and developed for use in automotive, aircraft, marine and other environments for which efficiency claims relate predominantly to the power controlling element and dissipation of energy in the form of heat resulting from unused voltage drop occurring across this element with dimmed lamp controller settings. These methods have adequately provided solutions to reduce such inefficiency which primarily limits the current available without heat sinking and component specifications becoming excessive. The approach generally utilizes a pulse width modulated voltage supply to the lamp(s) at such repetition rate as to emulate a linear, non pulsating direct current of reduced voltage to the lamp(s), effecting a dimmed light output, free from any perceivable flicker or pulsation of intensity, and yet maintain reduced energy dissipation by the controlling device.
These methods address needs basic to illumination control, but consideration of current reduction are secondary in importance. Also, the operating voltage of devices of the prior art is normally in the 10 volt or higher range as is customary to service lamps needing illumination level control, as is the case with instrument panel lighting (U.S. Pat. Nos. 5,113,180, 4,368,406, 4,358,714). And efficiency, although improved, nonetheless is only with respect to component rating; little has been directed toward the objective of optimizing the lumen/watt efficiency, which becomes of importance when dealing with portable or emergency lighting utilizing battery supplies of limited electrical capacity. Furthermore, low voltage direct current dimmers used in two wire configuration have, to our knowledge, not been developed; only in alternating current applications are such disclosed (U.S. Pat. Nos. 4,954,768, 4,876,498).